Air displacement pipetters with disposable pipette tips have been used in the medical and laboratory industries for many years. The main reason for such continual acceptance comes from the fact that after each use the pipette tip has traditionally been disposed of thereby limiting the possibility of cross contamination between samples. However as tests become more critical and the need to perform many tests from a limited amount of sample quantity became important, laboratory technicians have begun to have problems. These problems or errors could be contributed to operator use or fatigue, which often causes splashing of the sample. The sample could also aerosol during aspiration of the fluid, or the fluids contaminated gases can flow through the pipette tip upward into the calibrated barrel in the form of air borne contaminates. Even the smallest amount of dispensing error causing volume discrepancy or particles left behind on the barrel of the pipetter from previous tests can invalidate, or skew the evaluations of new test samples causing hours or even days of laboratory research to be wasted.
Users of porous plastic filter tips have also encountered problems with the accuracy of the amount of sample drawn into the pipette tip, arising from the requirements of the plastic sintering and molding process. Sintering does not produce a consistent size pore, such plugs are identified by an average or median pore size, a theoretical void volume within the filtered plug. Due to these variations, each pipette tip will have a different draw rate of fluid, which introduces inaccuracies into the amount of sample drawn into these types of filtered pipette tips. A researcher's work requires a high degree of volume consistency between samples and when hundreds of filtered or unfiltered pipette tips are used in just one procedure or test, the work may be invalid because of the inaccuracies in these sample volumes due to the precision and accuracy of the volumes dispensed. This is sometimes due to operator fatigue because of the excessive amount of force required to install and replace the disposable pipette tips.
Usually, in mounting a pipette tip on a mounting shaft of a pipetter, a user, exerting a downward force of between twelve and fifteen pounds, drives the mounting shaft axially into the pipette tip a distance which to the user seems sufficient to create a fluid tight seal. On occasion, in a mistaken attempt to improve the seal, a user will exert a downward insertion force from eighteen to twenty-five pounds. Since most pipette tips are formed of a relatively rigid plastic material such as polypropylene, the annular stretching of the pipette tip required to accommodate movement of the pipette tip onto the pipetter barrel is minimal. The inner surface and side walls of the proximal portions of most pipette tips are axially tapered at a one to one and a half degree greater angle than the distal end of the pipette tip mounting shaft and form an axially elongated frusto-conical annular sealing band. The sealing band is dimensioned to stretch outwardly (“hoop stretch”) as the distal end of the elongated generally conical pipetter barrel mounting shaft is forced into the proximal end of the pipette tip to firmly seat the tip on the barrel and to create an axially elongated annular fluid tight seal between the sealing band and the pipetter Barrel. The axial forces which must be exerted on a conventional pipetter to achieve such a positioning of the pipette tip on the pipetter barrel mounting shaft normally exceed twelve and may be as great as twenty pounds, which is difficult for many pipette tip users to generate. Of course, with most pipette tip designs, the greater the axial force exerted in seating a pipette tip on a pipetter barrel, the greater the force required to eject the tip from the barrel-mounting shaft.
In addition, the more firmly a pipette tip is mounted or wedged on the barrel of the pipetter, the greater the axial force which a pipetter user must generate by thumb and hand action to eject the pipette tip from the barrel when a tip replacement is desired. In practice, it is not uncommon for axial forces exceeding twelve pounds to be generated by the pipetter users thumb and hand in driving a pipette tip from a mounting shaft. Over several and repeated ejection operations, particularly with multi-channel pipetters where substantially greater axial ejection forces are required, the thumb and hand of the user become physically stressed often resulting in repetitive stress injury to the thumb and hand and in extreme cases, carpal tunnel syndrome. Accordingly, there is a need for an improved ergonomically designed disposable pipette tip which will easily and stably mount onto a pipetter barrel mounting shaft which may be subsequently ejected by a substantially reduced pipetter tip ejection force than existing standard disposable pipette tips in the market place today.
There also exist the need to accommodate the use of existing pipette tips in the marketplace with an ergonomic solution. Because pipette tips have been in existence for about 30 years there in lies a huge investment into injection mold tooling and capital equipment that helps produce hundreds of millions of many different size pipette tips with different configurations for many applications. These pipette tips have worked well over the years but now need to be modified and or updated to address the increase usage and fatigue problems found in the industry. This of coarse becomes cost prohibitive due to the high cost of tooling replacement for these multi-cavity tools that can easily cost upwards of $100,000.00 for one size only and can take over 4 months to produce.
As samples have become smaller and more valuable there exist a need to aspirate these sample liquids from the bottom of narrow neck containers or small diameter tubes. Examples of such containers are centrifuge tubes or test tubes where pipette tips are utilized to aspirate sample volumes for further evaluations. As such a pipette tip is inserted into such a tube, the end of the pipetter to which the pipette tip is mounted and the tip ejector mechanism of the pipetter are moved adjacent to and often contact a sidewall of the tube. This results in the undesired transfer of fluids or other contaminates from the sidewall to an outer surface of the tip ejector mechanism or pipetter barrel. Such transfer can result in contamination of the pipetter and cross contamination of subsequent samples if the tip ejector and outer surface of the pipetter are not cleaned and/or sterilized before reuse. Accordingly, there is a need for an improved ergonomically designed barrel adapter that will also extend the overall pipette tip length and will easily and stably mount onto a pipetter barrel mounting shaft which may be subsequently ejected by a substantially reduced pipetter tip ejection force.
For a better understanding of the invention and how this new ergonomic pipette tip and adapters overcome these disadvantages, reference is made to the following Summary, Description of Drawings and the Detailed Description of Invention.